1302-C - Drug Targeting of Novel Antimicrobials in the Methylerythritol Phosphate Pathway: Utilizing a Combination of In Silico and In Vitro Screening Methods

Tuesday, February 6, 2018

2:00 PM - 3:00 PM

Antibiotic resistance is a global problem, and the search for new antibiotics or bacterial targets continues to be a fruitful area of research. Two unrelated essential pathways exist in nature for the biosynthesis of isoprenoid metabolites, which include the methylerythritol phosphate (MEP) pathway, unique to bacteria, and the mevalonate (MVA) pathway used by humans. This makes the individual enzymatic steps of the MEP pathway attractive for the development of new antibiotics targeted against them, as few inhibitors of this pathway have been described. We produced an enzyme inhibition assay for MEP synthase (aka deoxyxylulose phosphate reductoisomerase, DXR), an early enzyme in the pathway, to be utilized in conjunction with an in silico screen to identify potential DXR inhibitors from an in-house compound collection.

We performed a structure-based drug screening project with Hudson Robotics (Springfield, NJ) using the OpenEye ROCS computational software package to virtually screen in silico a set of >150,000 compounds against the DXR enzyme of the MEP pathway. The in silico screening identified 189 potential DXR inhibitors, indicative of potent binding characteristics, which were screened in the DXR inhibitor assay using the methods provided. The compounds were supplied and custom plated from Frontier Scientific Inc.’s compound repository of >150,000 compounds for the study of druggable and enzymatic targets. The DXR inhibition assay, utilizing purified recombinant DXR in a coupled enzyme assay, was used to evaluate the compounds in vitro. The assay was optimized and the positive control fosmidomycin gave an IC50 of 150 nM similar to inhibitory values described previously. Two of the 189 test compounds showed modest inhibition of 5-10% at 100 µM with a third compound inhibiting 32% of DXR activity at this same concentration.

From this work, we identified three potentially active compounds that share a common functional group and pharmacophore. A next step is hit to lead identification in a genetically-engineered whole-cell based (Salmonella typhimurium) phenotypic screen to identify compounds that selectively inhibit the MEP pathway.

Our work highlights the potential of a unique discovery platform targeting the bacterial MEP pathway for the identification of novel antibiotics.

Leland J. Johnson

A member of the research and development team at Echelon Biosciences, Inc. Involved in the development of biological assays, immunological assays, drug screening, and research reagent development in the biological field.